The primary hypothesis to be tested is that a compound(s) of luteal origin acts in conjunction with progesterone to initiate renewed embryonic development and implantation in the ferret and in a species exhibiting an obligate delay of implantation. The first objective is to determine the chemical nature (lipid or protein) of the ovarian factor, other than progesterone, which induces implantation in ferrets. This will be accomplished by extracting the proteins and lipids from ovaries obtained from ferrets on the eighth day of pregnancy and testing the unfractionated and fractioned lipids and proteins for their ability to induce implantation in ovariectomized (Day 6) progesterone-treated ferrets and in intact spotted skunks with delayed implanting blastocysts. After the general chemical nature of the ovarian implantation factor is determined, attempts will be made to further characterize or identify the compound(s). Attempts will be made to verify that corpora lutea (CL) are a source of the compound, by culturing day eight CL obtained from ferrets with labeled precursors and then subjecting the conditioned culture medium to the same fractionation procedure which produced a biologically active product capable of inducing implantation. Lastly, an attempt will be made to determine whether the ovarian implantation factor stimulates embryonic development by acting directly on the blastocyst or indirectly through its action on the uterus. This will be accomplished by flushing the blastocysts from the uterus in situ and comparing changes in blastocyst diameter, 14C-glucose utilization and synthesis of protein, RNA, and DNA after short-term culture in the presence or absence of varying concentrations of the partially purified ovarian factor. The ovarian factor will likewise be administered to these same animals (whose uteri now lack blastocysts) for several days, and the uteri examined for changes in incorporation of 3H-uridine and 3H-thymidine into RNA and DNA. The long term goal of the proposed research is to define the mechanisms by which hormones of the anterior pituitary and ovary interact in controlling the cessation and the subsequent reinitiation of embryonic development in mammals exhibiting an obligate delay of implantation.